Frame synchronization apparatus

A frame synchronization apparatus is applied to the TDMA (Time Division Multiple Access) communication system, particularly, where a plurality of transmission rates are available. The frame synchronization apparatus calculates correlations between sampled sequences of a received signal and an assigned sync sequence during the longest or shortest frame period in the plurality of transmission rates. The apparatus stores positions where the correlations exceed a given threshold. Then, the apparatus sets a search gate at a position after a lapse of the longest or shortest frame period from each of those positions. The apparatus calculates correlations between the sync sequence and sampled sequences of the received signal for all the search gates. The actual transmission rate is determined from the plurality of transmission rates based on a time interval of positions where the correlations beyond a second threshold were detected. Synchronization is thus established.

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Claims

1. A frame synchronization apparatus of a receiver for use in a TDMA communication system which has a plurality of transmission rates and which receives data at transmission rates that are unidentified at a time of receipt of the data, comprising:

correlation means for correlating between an assigned sync sequence and a received sync sequence; and
mode control means, connected to the correlation means, for switching between a first mode and a second mode, wherein the mode control means memorizes all positions at which correlations are beyond a first threshold, and in the second mode the mode control means determines the unidentified transmission rate of currently received data by comparing correlations with a second threshold.

2. A frame synchronization apparatus of a receiver for use in a TDMA communication system which has a plurality of transmission rates, comprising:

correlation means for correlating between an assigned sync sequence and a received sync sequence; and
mode control means, connected to the correlation means, for switching between a first mode and a second mode, wherein in the first mode the mode control means memorizes all positions at which correlations are beyond a first threshold, and in the second mode the mode control means determines frame synchronization by comparing correlations with a second threshold, wherein the mode control means memorizes the correlations during a longest frame period in the first mode, sets a search gate about each of the memorized positions, and determines whether the correlation of each search gate is beyond the second threshold.

3. A frame synchronization apparatus according to claim 2, wherein each of the search gates is set after the longest frame period of each of the memorized positions.

4. A frame synchronization apparatus according to claim 2, wherein each of the search gates is set after a shortest frame period of each of the memorized positions.

5. A frame synchronization apparatus of a receiver for use in a TDMA communication system which has a plurality of transmission rates, comprising:

correlation means for correlating between an assigned sync sequence and a received sync sequence; and
mode control means, connected to the correlation means, for switching between a first mode and a second mode, wherein in the first mode the mode control means memorizes all positions at which correlations are beyond a first threshold, and in the second mode the mode control means determines frame synchronization by comparing correlations with a second threshold, wherein the mode control means memorizes the correlation during a shortest frame period in the first mode, sets a search gate about the memorized position, and determines whether the correlation of the search gate is beyond the second threshold.

6. A frame synchronization apparatus of a receiver for use in a TDMA communication system which has a plurality of transmission rates, comprising:

correlation means for correlating between an assigned sync sequence and a received sync sequence;
first mode setting means for memorizing all positions at which correlations are beyond a first threshold during a predetermined period of time;
gate setting means for setting search gates about all of the positions memorized in a first mode;
second mode setting means for comparing the correlation with a second threshold about each of the search gates; and
determining means for determining a current transmission rate among the plurality of transmission rates.

7. A frame synchronization apparatus according to claim 6, wherein the first mode setting means memorizes the positions during a longest frame period, and the gate setting means sets the search gate after the longest frame period of each of the memorized positions.

8. A frame synchronization apparatus according to claim 6, wherein the first mode setting means memorizes the positions during a longest frame period, and the gate setting means sets the search gate after a shortest frame period of each of the memorized positions.

9. A frame synchronization apparatus according to claim 6, wherein the correlation means comprises:

a frequency offset estimator for estimating a frequency offset of a received signal;
a frequency offset compensator connected to the frequency offset estimator for compensating for a frequency offset of the received signal by using the estimated frequency offset provided from the frequency offset estimator; and
a correlation calculator for calculating the correlation between the assigned sync sequence and the received sync sequence of the received signal.

10. A frame synchronization apparatus according to claim 9, wherein the correlation means further comprises an estimate limiter provided at an output side of the frequency offset estimator.

11. A method for frame synchronization for use in a TDMA communication system which has a plurality of transmission rates, comprising the steps of:

(a) in a first mode:
calculating first correlations between an assigned sync sequence and received sync sequences for a predetermined period;
memorizing all positions at which the correlations are beyond a first threshold; and
setting a search gate about each of the memorized positions;
(b) in a second mode:
calculating second correlations between the assigned sync sequence and received sync sequences for all the search gates; and
determining whether the second correlation is beyond a second threshold, thereby obtaining frame synchronization.

12. A frame synchronization apparatus of a receiver for use in a TDMA communication system which has a plurality of transmission rates, comprising:

correlation means for correlating between an assigned sync sequence and a received sync sequence; and
mode control means, connected to the correlation means, for switching between a first mode and a second mode, wherein in the first mode the mode control means memorizes all positions at which correlations are beyond a first threshold, and in the second mode the mode control means determines frame synchronization by comparing correlations with a second threshold, wherein the mode control means memorizes the correlations during a longest frame period in the first mode, in the second mode sets a search gate about each of the memorized positions and determines whether the correlation of each search gate is beyond the second threshold.

13. A frame synchronization apparatus according to claim 12, wherein each of the search gates is set after the longest frame period of each of the memorized positions.

14. A frame synchronization apparatus according to claim 12, wherein each of the search gates is set after a shortest frame period of each of the memorized positions.

15. A frame synchronization apparatus of a receiver for use in a TDMA communication system which has a plurality of transmission rates, comprising:

correlation means for correlating between an assigned sync sequence and a received sync sequence; and
mode control means, connected to the correlation means, for switching between a first mode and a second mode, wherein in the first mode the mode control means memorizes all positions at which correlations are beyond a first threshold, and in the second mode the mode control means determines frame synchronization by comparing correlations with a second threshold, wherein the mode control means memorizes the correlation during a shortest frame period in the first mode, in the second mode sets a search gate about the memorized position and determines whether the correlation of the search gate is beyond the second threshold.
Referenced Cited
U.S. Patent Documents
5121414 June 9, 1992 Levine et al.
5177740 January 5, 1993 Toy et al.
5408504 April 18, 1995 Ostman
5539751 July 23, 1996 Sabel
5590160 December 31, 1996 Ostman
Patent History
Patent number: 5680421
Type: Grant
Filed: Feb 22, 1996
Date of Patent: Oct 21, 1997
Assignee: Oki Electric Industry Co., Ltd. (Tokyo)
Inventors: Haruhiro Shiino (Tokyo), Norio Yamaguchi (Tokyo), Toshimichi Naoi (Tokyo), Ryoichi Miyamoto (Tokyo)
Primary Examiner: Stephen Chin
Assistant Examiner: Betsy Lee Deppe
Law Firm: Rabin, Champagne & Lynt, P.C.
Application Number: 8/604,832
Classifications
Current U.S. Class: Synchronizer Pattern Recognizers (375/368); Synchronization (370/350); Frame Length (370/470)
International Classification: H04L 700;